Conventionally, a transmissive mask whose back surface is composed of glass (Qz) has been used as a photomask. Organic matter is difficult to adhere to Qz due to its surface condition, so that adhesion of particles to the back surface does not substantially arise as a problem. On the other hand, an EUV mask (EUV exposure mask) is a reflective mask, so that an exposure process needs to be performed in a state where the EUV mask is electrostatically chucked. Therefore, a conductive film is formed on the back surface of the EUV mask. For the conductive film, a material, to which organic particles are easy to adhere, is often used, and adhered organic particles are difficult to clean in a cleaning process thereafter. If organic particles are adhered to the conductive film, the EUV mask distorts when the back surface of the EUV mask is electrostatically chucked, so that a dimension or a position of an exposed wafer pattern is misaligned from a desired value.
Moreover, when manufacturing the EUV mask, if a film is attached to the back surface of the EUV mask, poor drying (droplet residue) occurs after a development treatment. Then, impurities including carbon in the air adhere to liquid remaining on the back surface, which results in contaminating the back surface of the EUV mask. Therefore, a countermeasure is needed against contamination (particles or droplet residue defects) of not only the front surface but also the back surface in the EUV mask.